In a surprise announcement, Arapahoe County District Attorney George Brauchler, the Republican whom Colorado and national party leaders had been counting on to challenge Democratic Sen. Michael Bennet, said Wednesday that he will instead run for re-election, according to reports from Colorado's 9News .

"There were serious family health issues that just recently came up," a GOP operative told CQ Roll Call.

Brauchler alluded to his family in a letter obtained by 9News.

"Despite the overwhelming support and encouragement I received over the past few weeks, I have decided that now is not the right time for me and my family for me to make a run for the United States Senate," Brauchler wrote.

A Democratic polling firm conducted a poll for End Citizens United earlier this month that showed Brauchler trailing Bennet in a hypothetical matchup by only 3 points , within the margin of error.

Brauchler's decision leaves the party without a top-flight challenger to take on the two-term Democratic incumbent, who's already been amassing an impressive war chest for his re-election.

"Well I think there are some potentially strong candidates in the party that will now take a look at it," said Dick Wadhams, former two-time chairman of the state party. Wadhams suggested that this time next year outside spending could be "the great equalizer." "While I think a lot of attention has been focused on George, I don’t think it changes the fundamental dynamics," he added. Throughout the party's struggle to lock down a candidate, Republicans have often pointed to freshman Sen. Cory Gardner, who didn't get into the 2014 Senate race until March of that year, to illustrate that there's still time for a strong candidate to enter the race.

But even Wadhams acknowledged that the clock is ticking.

"Senate campaigns are major efforts. It takes time to gear them up," he said. The party is not without candidates, but none are considered to be as strong as Brauchler would have been.

Businessman Robert Blaha, who lost a 2012 primary to 5th District Rep. Doug Lamborn, told CQ Roll Call earlier this month he's likely to launch a bid soon. The same poll conducted for End Citizens United gave Bennet only a 4-point lead over Blaha.

Earlier this year, Greg Lopez, the former director of the Small Business Administration in Colorado, announced that he would run. El Paso County Commissioner Darryl Glenn declared his candidacy in January.

3rd District Rep. Scott Tipton has not ruled out mounting a bid. Michael Fortney, a campaign consultant to Tipton, reiterated Wednesday evening that the three-term congressman is "not closing doors on anything," but, as of now, is still planning to run for re-election.